1. Field of the Invention
The present invention relates to a transmission line and filtering module thereof, and more particularly, to a transmission line and filtering module thereof for suppressing conduction and coupling noises without using a ferrite core.
2. Description of the Prior Art
In general, a computer system, such as a personal computer, a television, a mobile phone and so on, can link to peripheral devices, for example, link the computer system to a head-set, a microphone or a television dongle through a transmission line, to expand additional functions.
Also, most governments promulgate related regulations and standard test procedures for ensuring an ElectroMagnetic Compatibility (EMC) between the peripheral devices and the computer system. A radiation emission test is one of test items in the regulations, which is to test whether an operating electric product emits excess electromagnetic waves or noise to interfere with its own or other electronic products' functions.
However, despite that the transmission line is normally used for transmitting signals, sometimes it may become a medium for transmitting noises, which causes that the electronic product emits excess noises. Specifically, please refer to FIG. 1, which is a schematic diagram of a computer system 10. The computer system 10 includes a host computer 11 (e.g. television), a peripheral device (e.g. television dongle) and a transmission line 13. When the peripheral device 12 links to the computer system 10 through the transmission line 13, a conduction noise, which is denoted with a dashed line, may propagate between the peripheral device 12 and the host computer 11 through the transmission line 13 at the same time. Or, a space coupling path may be formed by the transmission line 13, such that a coupling noise, which is denoted with a solid line, may be radiated in the air. Traditionally, the conduction noise may be filtered out and suppressed by a filtering circuit disposed on a printed circuit board (PCB) of the peripheral device 12, which may prevent the conduction noise from entering the transmission line 13. On the other hand, the coupling noise may be suppressed by a ferrite core winded around the transmission line 13, wherein the ferrite core is magnetically conductive to form a high-frequency resistor in the air to attenuate a magnetic field intensity of the coupling noise, so as to suppress the coupling noise.
In practice, if the coupling noise is too strong to be suppressed by the filtering circuit disposed on a printed circuit board, only the ferrite core can suppress the coupling noise. However, the ferrite core has some disadvantages such as large sizes and higher costs than the filtering circuit. Meanwhile, the electronic product becomes more and more complicated and the noises may cover a wide frequency range, which results in that the ferrite core cannot suppress the noises in such a wide frequency range.
Therefore, how to provide a signal transmission line for suppressing the conduction and coupling noises without using the ferrite core to reach small sizes and reduce cost, has become a topic in the industry.